Fluoroelastomer compositions which cure by an addition reaction between alkenyl groups and hydrosilyl groups are known in the art. Related compositions imparted with self-adhesiveness by additionally including, as a third component, an organopolysiloxane bearing hydrosilyl groups and epoxy and/or trialkoxysilyl groups, have also been proposed (JP-A 9-95615). Addition of carboxylic anhydride to these compositions results in compositions with improved adhesion to polyphenylene sulfide resins and polyamide resins as disclosed in JP-A 2001-72868.
By brief heating, these compositions can be cured and at the same time, bonded to a variety of substrates. The cured products have excellent gasoline resistance, oil resistance, chemical resistance, heat resistance and low-temperature properties, low moisture permeability and excellent electrical characteristics. Such compositions are used in sealing, potting and coating applications within a variety of industrial fields where these properties are required.
Particularly in the coating application, the compositions are often used in solution form after they are diluted with fluorinated solvents. Suitable fluorinated solvents which are used to form coating solutions include 1,3-bis(trifluoromethyl)benzene, Fluorinert® (3M), perfluorobutyl methyl ether, and perfluorobutyl ethyl ether.
Use of these solvents alone, however, gives rise to a problem that a uniform solution is not obtained, or even when a uniform solution is obtained, a coating resulting from the solvent volatilizing off becomes uneven in appearance or thickness. For example, when a solution is prepared by combining the aforementioned curable composition with one of the aforementioned solvent and applied as a protective coating onto a substrate having electric and electronic parts mounted thereon, some cured coatings have a mottled appearance and a varying thickness.
In the application of protective coatings on electric and electronic parts, there is a need for a coating composition in which a fluoroelastomer composition exhibiting good adhesion to a variety of substrates of metals and plastics is uniformly dissolved and which can form a cured coating having a uniform and smooth appearance after drying.